Catalyst for purification of exhaust gases

Abstract

A catalyst for the purification of exhaust gases contains a catalyst carrier with a first coat layer formed on a surface of the catalyst carrier and with a second coat layer formed on a surface of the first coat layer. The first coat layer contains an active alumina and a catalyst component comprised of a noble metal such as platinum and rhodium and at least one of zirconium oxide, lanthanum oxide and barium oxide is immobilized on particles of the active alumina, and the second coat layer contains an active alumina, cerium oxide and a catalyst component comprised of another noble metal such as palladium. The oxides of zirconium, lanthanum and/or barium can prevent the alumina particles from aggregating together due to heat, thereby improving heat resistance of the catalyst.

What is claimed is: 
     
       1. A catalyst for the purification of exhaust gases consisting essentially of a catalyst carrier with a first coat layer formed on a surface of the catalyst carrier and with a second coat layer formed on a surface of the first coat layer; wherein the first coat layer consists essentially of an active alumina and a catalyst component comprised of a noble metal and at least one of zirconium oxide, lanthanum oxide and barium oxide is immobilized on particles of the active alumina;   the second coat layer consists essentially of an active alumina, cerium oxide and a catalyst component comprised of another noble metal, wherein a ratio of the weight of the active alumina to cerium oxide ranges from approximately 95 to 5 to approximately 70 to 30; and   wherein said zirconium oxide, lanthanum oxide or barium oxide is contained in an amount ranging from 1% to 10% by weight based on the weight of a total wash coat of the first coat layer and the second coat layer.   
     
     
       2. A catalyst as claimed in claim 1, wherein the noble metal contained in the first coat layer is platinum and/or rhodium. 
     
     
       3. A catalyst as claimed in claim 1, wherein said another noble metal contained in the second coat layer is palladium. 
     
     
       4. A catalyst as claimed in claim 1, wherein said noble metal contained in the first coat layer is platinum and rhodium and the another noble metal contained in the second coat layer is palladium. 
     
     
       5. A catalyst as claimed in claim 3, wherein cerium oxide contained in the second coat layer is contained in the amount ranging from 5% to 30% by weight based on the weight of the catalyst carrier and the first coat layer. 
     
     
       6. A catalyst as claimed in claim 1, wherein zirconium oxide, lanthanum oxide and barium oxide are immobilized on the particles of the active alumina. 
     
     
       7. A catalyst as claimed in claim 1, wherein zirconium oxide and lanthanum oxide are immobilized on the particles of the active alumina. 
     
     
       8. A catalyst as claimed in claim 1, wherein zirconium oxide and barium oxide are immobilized on the particles of the active alumina. 
     
     
       9. A catalyst as claimed in claim 4, wherein zirconium oxide, lanthanum oxide and barium oxide are immobilized on the particles of the active alumina.